Those tyres look absolutely finre, the balling on the edge is just a result of normal track ware and the lump in the centre are just pick up from others shed rubber. There is plenty of life in them but check to see if their profile is even as they can wear more on one side on a track with more of one corner (left or right).

I would say however that mixing the tyre makes can cause a few handling problems as front and rear tyre profiles are designed to compliment each other and each manufacturer has their own particular profile. Not sure if it is the same over there but here the Alpha 10 has been discontinued so i would consider match the front to the rear you have.

as a rough guide i tend to through 2 rears to 1 front.